Substituted 6-hydroxychroman-2-carboxylic acids have been used in the synthesis of vitamin E. Natural vitamin E has a 2 R configuration. However, present commercial synthesis of this compound has yielded an enantiomeric mixture at the 2-position. Some synthesis routes for vitamin E involve coupling a chroman moiety containing one asymmetric center with a C.sub.14 or C.sub.15 alkyl chain having two asymmetric carbon atoms. Enantiomerically pure chroman compounds required for the synthesis of natural vitamin E have been derived by classical resolution of their racemic mixtures or by steroselective synthesis from a chiral precursor [A Novel Synthesis of (2 R, 4' R, 8' R-alpha-Tacopherol (Vitamin E). Construction of Chiral Chromans from an Optically Active, Nonaromatic Precursor, N. Cohen et al. J.A.C.S. 101, 6710 (1979) and cited references]. 6-hydroxychroman- 2-carboxylic acid or 2-acetic acid have been resolved for optically active synthesis. Preparation of optically active acids and alcohols by stereospecific hydrolysis of esters or esterification of acids and alcohol by lipases and esterases have attracted wide attention and utilization [Enzymes in Synthesis, J. B. Jones, Tetrahedron 42, 3351-3403 (1986) and references cited therein; Enzymes in Organic Synthesis, A. Akiyama et al., Chemtech, 627-634 (1988); Enzymatic Catalysts in Organic Synthesis, C. H. Wong, Science, 244, 1145-1152 (1989)]. Enantiomerically pure chroman carboxylic acids, apart from their use in the synthesis of vitamin E in its natural form, have been used as antioxidants [6-Hydroxychroman-2-carboxylic acids: Novel Antioxidants, J. M. Scott et al., J. Am. Oil Chem. Soc. 51, 200-203 (1974)] and as drug intermediates [3,4-Dihydro-2H-1-benzopyran-2-carboxylic Acids and Related Compounds as Leukotriene Antagonists, N. Cohen et al., J. of Med Chem. 32, 1942-1860 (1989)].
In order to satisfy the need for optically active hydroxychroman-2-carboxylic acids, new methods of preparation are required.